Telephone system



Sept. 19, 1933. J. wlcKs TELEPHONE SYSTEM Original Filed Aug` 17, 1931 4 Sheets-Sheet l Sept. 19, 1933. J. wlcKs TELEPHONE SYSTEM Original Filed Aug. 17, 1931 4 Sheets-Sheet 2 Im-ria?- .Juhn D'Jicks Sept. 19, 1933. J. wlcKs TELEPHONE SYSTEM Original Filed Aue. 17, 1931 4 Sheets-Sheet 3 A .JIU

EMA 1S.

Original Filed Aug. 17. 1931 Sept. 19, 1933.

Patented Sept. 19, 1933 TELEPHONE SYSTEM John Wicks, vOak Park, Ill., assigner, by mesne assignments, to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation of Y Delaware Application August 17,1931, serial No. 557,566

Y Renewed November 17, 1932 21 claims. (o1. 179-;16) Y The present invention relates to telephone systems in general, but is concerned more particularly with telephone systems employingautol matic switches to set up the telephone connecjtions; and the main object is the production of a new and improved automatic telephone system wherein the setting impulses are delivered directlyY to the operating magnets of the automatic switches from the relays of the rst trunk line or numerical switch of a train rather than from separate linerelays individual tothe several switches, respectively, of a train.

General description l5 Asis well known, automatic telephone systems employing step-by-step switches fall into two general classiiications, depending upon the method used for delivering the setting impulses to the magnets of the switches. The more-com- 2@ lmon method is to employ a quick-acting line relay and a slow-acting release relay at each numerical switch, through the contacts of which impulses are delivered to position the associated switch. A number of so-called direct-pulsing systems have been developed, however, which employ the usual line relayand slow-acting release relay at the iirst switch ofthe train, but deliver impulses directly to the magnets of the subsequent switches in the train by way of one or both of the talking conductors extending through the connection established to the subsequent switches. f

I'he present invention is concerned with im-` r provements in systems of the second class, briefly outlined above, and it contains the following outstandingfeatures:

l. In order to avoid the possibility of disturbances being set up in surrounding talking conductors responsive to the fairly heavy .impulses of current delivered to the operating magnets of succeeding switches through the talking conductors, circuit arrangements are provided for operating the magnets of the switches succeeding the first-selector repeater over a loop circuit including the two talking conductors in` series,

maintaining a sufficient current flow over the return conductor between impulses to maintain the series relay operated continuously throughout a seriesvof impulses. By this arrangement, currentpimpulses are transmitted over the two talking conductors in series to operate the operating magnet connected to one talking conductor, while between impulses the holding current is transmitted over the other talking conductor to maintain the series relay operated, whereby the changeover operation is separately controlled over the second talking conductor.

2. In order to realize the greatest possible economy without sacrificing reliability, the number of relays needed at the intermediate selectors and at the connectors have been reduced toa minimum by providing circuit arrangements whereby the functions of the relays eliminated are taken over bythe remaining relays. In the connector,` the ring-cut-ofi relay is used during the setting operation of the connector to control thechangeover from the vertical movement to therotary movement, and the busy relay is brought into play again when the calling sub-v scriber replaces his receiver before the called subscriber does, and is operated over the called line to ymaintain the connector operated as long as the receiver is off the hook at the called substation, while the preceding switches in the train are released responsive to the receiver being replaced atv the calling substation. In the-intermediate selectors, the relays have been reduced to a series relay for changing over from the vertical movement` to the rotary4 movement and a switching relay for connectingv up the wipers at the end of the rotary movement, while the function of the release relay is taken over by the combined action of the two relays, which are both operatedto close a circuit for the release magnet when the holding potential is removed from the release-trunk conductor.

3. An additional feature of the present arrangement is that no special circuit-altering arrangement need be made in the rst selector repeater when'an inter-oice trunk line is taken for use, as circuit arrangements are provided for operat# ing an impulse-receiving relay in the incoming selector in the called office over the rst talksov ing conductor in the same way that an operating 05 magnet is operated over the rst talking conductorin a local connection. The holding of the connection, together withthe giving of supervision,A is accomplished over the second talking conductor to which a` high-resistance line relay is L ll() connected in the 1ncom1ng selector repeater, be-

- first impulse.

ing supplied with battery potential in order to hold up in series with the ground-connected lower winding of the back-bridge relay of the first selector repeater.

4. A special feature of the inter-ofce repeating arrangement is concerned with the provision of a ground connection to the second talking conductor in the selector repeater in order to enable the repeating relay in the distant incoming selector repeater to operate at the beginning of the rst impulse, in combination with circuit arrangements in the incoming selector repeater for applying ground potential thereat in shunt of the ground connection to the lower vtalking conductor in the rst selector repeater,thereby providing a loop circuit for the transmission of all impulses of a series following the beginning of the It will be understood, of course, that a loop impulsing circuit is considered to be more desirable in general than a ground-return impulse circuit because of the likelihood of diferences in ground potential existing between two offices of a system.

Other objects and features of the invention, for the most part incidental to the objects and features hereinbefore enumerated and having to do mainly with the provision of suitable circuit arrangements for carrying out the required operations in a system such as outlined hereinbefore, will become apparent upon a further perusal of the specication.

Description of drawings Referring now to the accompanying `drawings comprising Figs. 1-4, they show by means of the usual circuit diagrams a sucient amount of apparatus in a telephone system embodying the Yfeatures of the invention to enable the invention to be understood. In order for the drawings to be understood best, Figs. 1-3 should be arranged in order, with Fig. 4 above Fig. 2. When the drawings are thus arranged, they show apparatus which may be involved in setting up a connection from the line of substation A1, Fig. 1, to` the line of substation A2, Fig. 3, in the same -ofce and to the line of substation A3, Fig. 4, ina distant oiiice. l

Fig. 1 shows the office selector OS (a rst selector repeater) which is accessible to line switches such as the line switch LS of substation A1.

Fig. 2 shows the thousands selector Th.51 andk the hundreds selector H51 (intermediate selectors). The hundreds selector H51 has two sets oi wipers and is provided with a wiper-switching relay 253 to control the selection of wipers during the rotary movement, thereby giving Vaccess to twenty trunks on each level of bank contacts.

Fig. 3 shows the connector C1, which is accessible by way of one level of the hundreds selector H51 and which has access to the line of substation A2. Y

Fig. 4 shows the thousands selector Th.52 (an incoming selector repeater) in a distant office, together with the hundreds selector H52 and the connectorCZ, which has access to the line of substation AB. The switches H52 andJC2 are indicated by dotted rectangles, but they maybe similar to the switches H51 and C1, respectively. The numerical switches used in the present system are assumed to be two-motion switches of the regular Strowger type, vwhile the line switch LS is assumed to be a rotary line switch of the usual construction'and having the usual circuit arrangement.Y For this reason, the relays associated with the line switch LS are not shown.

Detailed description The invention having been described generally, a detailed description of the operation of the apparatus shown will now be given. For this purpose it will be assumed that the subscriber at substation A1, Fig. 1, desires to converse with the subscriber at substation A2, Fig. 2.

Local call from substation A1 to substation AZ Seieing the o17ice selector OS In the `ofrice selector O5, line relay 111 now operates over conductors 102 and 103 of the calling line and through contacts of relay 112. Upon operating, line relay 111 closes a circuit at its inner armature `for release relay 114 in `series,

with the resistance element 115; the inner armature of relay 111 being grounded by way of the lower armature of relay 116 and oli-normal spring 123. When relay 114 operates, it closes a locking circuit for itself at its inner lower armature; applies ground potential by way of the low-resistance lower winding of relay 112 to the Windings of switching relay 118 at its inner upper armature; opens a point in the circuit of release magnet 120 at its upper armature; applies ground potential at its middle upper armature by way of contacts of relay 116 to,release trunk conductor 109, thereby closing a holding circuit for the line switch LS; prepares an impulse-repeating circuit at its lower armature; and at its middle lower armature it closes a circuit by way of contacts of series relay, 117, inner lower armature of relay 118, and the off-.normal spring 127 and its lower contact for the meter-control relay 116. Relay 116 thereupon operates and prepares a locking circuit for itself at its inner lower armature; removes the ,normal ground connection from the inner armature of line relay 111 at its lower armature and vapplies ground potential to the supervisory `1 Aconductor 133; and at its upper armature itjshifts the connection between the middle upper armature of relay 114 and conductor 109 so that it includes the normally closed contacts controlled by the upper armature of back-bridge relay 113, preparatory to operating the marginally adjusted meter M when the call is answered.

Dial tone The tone-start relay 137 is operated over the common tone-start conductor-135 in series withA relay 116, thereby starting the various tone-generating devicesA of the exchange into operation. Current now ows from the dial-tone generator (not shown) by way of the common dial-tone' iiow from the dial-tonegenerator, the calling subscriber starts to dial the digits in the desired number.

Setting the oce selector OS when the mst digit is diaued, the circuit of line relay 111 of the oice selector OS is opened momentarily the desired number of times at the n contacts of the calling device on the calling line. .10

Each time the circuit is opened, line relay 111 falls back momentarily.' Each time line relay 111 falls back, it places a shunt around release relay 114 at the normally closed contacts controlled-by its inner armature, thereby closing a circuit through the inner upper contacts of the meter control relay 116 for the series relay 117. Relay 117 operates responsive 'to the rst shunt beingplaced around relay 114, and it remains operated throughout the series of impulses, owing to the shunting eiect of the resistance element 115 and owing to the current-flow through re-V lays 117 and 114 in series, as well as because of theretarding elect of the copper collar provided on the heel end of the core of the relay, as indicated by the shaded lower portion. ItA will be understood, of course, that relay 114, being locked energized at its inner lower armature, does not fall back during the series of deenergizations of relay 111 because of the. local circulating curlrent through its winding and through the contacts of line relay 111 while the relay is shunted; As a further result of each deenergization of line relay 111, a connection is made between the .upper and lower talking conductors on the wiper 'side of the talking condenser at the normally closed contacts controlled by the lower rarmature of line relay 111. This connection includes the lower armature of release relay 114. The verti- ,cal magnet 122 responds each time this connec- Ation is made between the two talking conductors,

since it is connected to the wiper side of the upper talking conductor through the upper contacts of relays 118 and 112, while ground potential is supplied to the wiper side of the lower talking 'conductor by way of the middle lower armaturev of relay 114, inner lower armature of the now# energized series relay 117, lower armature of relay 118, and the lower armature and resting contact of relay 112. For convenience in following the circuit of the Vertical magnet 122, the cornplete circuit may be traced as follows:

From ground by way of the middle lower armature or" relay 114, inner lower armature of the .now-operated seriesrrelay 117, lower armature of relay 118, lower armature, normal, of relay 112, normally closed contacts controlled by the lower armature of relay'lll, lowerarmature of relay 114,' upper armature of relay 112, upper armature of relay 118, and vertical magnet 122 to battery. y

By the operation of vertical magnet 122, the

wipers'129-131 are raised step by step until theyr comertorest opposite the desired levelof bank contacts. It is to be noted that the upper and lower windings of back bridge relay 113 are disconnected at the` upper and lower armatures ofV the series relay 117 `during the transmission of impulses to the vertical .magnet thereby preventing a premature operation or relay 113.

When-the wipers 129-131 of the oice selectork OS are raised from their normal. position, offnorrnal spring 127 opens the initial circuit of the'r meter-control relay 116, but offfnormal spring 132 closes a locking circuit for relay 116-by way of'the lower contacts of.r back-bridge relay 113 and the inner lower armature of relay 116. y

At the end of the series of impulses, relay 117 falls'back, as the-normal ilow of current through and oli-normal springA 127 and its upper contact,. as well as the self-interrupting contacts of theA rotary magnet. By the .operation ofthe rotaryv magnet, the wipers 129- 131 are driven step by step across the bank contacts in the selected level, insearch of an idle trunk line. When an idle trunk line is reached, which trunk line, it will-be.

assumed, is the one comprising conductors 154-156, wiper 130 encounters a battery potential on the test contacts of the idle trunk line, closing a circuit for the upper windingV of switching relayA 118. The left-hand terminal of the upper wind, ing of switching relay 118 is supplied with ground potential by way of the low-resistance lower winding ofthe marginally adjusted switch-throughk relay 112 and the inner upper contacts of release relay 114. Battery potential is supplied to release trunk conductor 155 of the idle trunk line by way of overow spring 209 and its left-hand Contact,l

inner upper armature of relay 202, oir-normal spring 204, resistance 217, and the supervisoryY relay 215.

When switching relay 118 operates,iit opens the circuit of rotary magnet 139 at its inner lower armature so'as to stop the rotary movement of the switch, at the same time closing a locking circuit for its lower winding in series with the rotary magnet 139; it opens a point in the dial-tone circuit at its middle lower armature; short circuits its upper winding so as to apply ground potential moredirectly to the release-trunk conductor of the seized trunk line; and at its upper and lower armaturesit disconnects the upper and lower talking conductors from the circuit of vertical magnet 122 and extendsthern by way of wipers 129 and 131 and conductors 154 and 156 to the thousands selector Th.S1. Y

Settingy the thousands selector Th.S1 K

When the calling subscriber dials the second digit in the desired number, series relay 117 r sponds as before to the series of deenergizations of line relay 111. In addition, each deenergization of line relay 111 results'in a bridge being placed across wipers 129 and 131 at the lower contacts of the relay and through contacts of relay 114. This bridge, it will be noted, includes the resting contacts of the upper and lower armatures of relay 112, and the corresponding armatures of the operated switching relay 118. Each time this bridge is closed, Vertical magnet 206 operates therethrough and over conductors 154 and 156 in series,; ground potential being supplied to conductor 156.

by way lof the low-resistance lower winding of series relay 201 of the thousands selector Th. S1.

By the operation of vertical magnet 206, the wipers 211-213 of the thousands selector ThjSl are raised step by step until they come to rest opposite the desired level of bank contacts. Relay 201 operates responsive to current flow in its lower winding when the rst impulse of current is delivered to vertical magnet 206, and it remains operated throughout the series of impulses because of the shunting effect of the .ground connection to the lower talking conductor at the oice selector OS by way of the lower armature of series relay 117 and resistance element 126. Moreover, with relay 117 operated, a battery connection is made by way of thesomewhat higher resistance element 125 through the lower armature of line` relay 111 each time relay 111 reoperates at the end of an impulse. The current passing through resistance element 125 flows through the resistance element 126 and the lower winding of relay 201 in parallel. The current thus flowing over the lower talking conductor and through the lower winding of relay 201 between impulses is suilicient to maintain relay 201 operated throughout the series of impulses.

Itis to be noted that off-normal contacts 203, upon becoming closed when the wipers are raised from their normal position, close a circuit for the upper winding of series relay 201 and the lower winding of switching relay 202 in series, by way of the resistance element 210. No substantial current flows through theupper winding of relay 201 and the lower winding of relay 202 for the time being because, when off-normal spring 204 is allowed to shift from its normal position to open the circuit of supervisory relay 215, when the vertical movementstarts, it permits the associated normally open oir-normal contacts to close, thereby extending a ground potential from the release trunk conductor 155 to the junction of the lower winding of relay 202 and the resistance element 210, thereby shunting'the current-flow away from the lower winding of relay 202 and the upper winding of relay 201.

At the end of the series of impulses'constituting -the second digit, series relay 1170i the office selector OS falls back, removing Athe battery connection throughthe resistance element 125 from the lower talking conductor at its middle lower armature, at the same Vtimey shitingthe .lower talking conductor from in connectionwith resistance element 126 back to the lower winding of relay 113. When this occurs, the series relay 201 ofthe thousands selector Th.S1 falls back, thereby completing a circuit for rotary magnet 207 through the lower armature of switching relay 202 and off-normal contacts 208.y Magnet 207 now operates in a buzzer-like manner to advance the wipers 2li-213 over the bank contacts in the selected level in search of an idle trunk line.

When an idle trunk line is reached, the `trunk line comprising conductors 218-220, for example, the upper winding of switching relay 202 is energized responsive to wiper 212 encountering a battery potential on the test contact of the trunk line, supplied by way of conductor 219. Upon operating, relay/202 opens the rotary-magnet. circuit at'its lower armature, thereby terminating the rotary movement; closes a locking circuit for its lower 'winding in series with resistance element 210 atits inner lower armature; disconnects the incoming release-trunk conductor 155 from the junction of its lower winding and resistance4 element 210 in order to enable the locking circuitfor the lower winding to become effective, at the Sametime short circuiting its upper winding so as to place a more eiective guarding ground potential on the test wiperf212; and at its upper and lower armatures it disconnects the incoming talking conductors 154 and 156 from vertical magnet 206 and the lower winding of relay'201 and eX- tends them by way of wipers211 and 213 to the corresponding magnet and relay of the hundreds selector HSl.

It is to be noted that the ground potential supplied to the junction of the upper winding of relay 201r and the lower winding of relay 202 by the locking contacts of the latter relay prevents substantial current flow through relay 201, with the result that relay 201 remains in normal position.

In the hundreds selector HSL the application of ground potential to release-trunk'conductor 219 by way of wiper 212 results in current flow through the contacts controlled by overflow spring 221, inner upper armature of relay 252, off-normal spring 225, resistance element 259, the common supervisory conductor 263 and supervisory relay 264. Relay 264 thereupon becomes operated to indicate that a selector in the group containing the selector HSl is in a seized and unoperated condition.

Setting the hundreds selector HSI When the third digit is dialled, the current impulses are transmitted to vertical magnet 257 100,

series of impulses, it completes the circuit of 110.

rotary magnet 262, which has been prepared at off-normal contacts 261, whereupon rotary magnet 262 operates in a buzzer-like manner to drive the wipers across the bank contacts in the selected level.

When an idle trunk line is reached, relay 252 is operated through test wiper 267 or through test wiper 270 to seize the idle trunk. It is to be noted that the wiper switching relay 253 has its upper winding connected between test wiper 270 and the incoming release trunk conductor 219, by way of contacts controlled by the inner lower armature of relay 252. By this arrangement, wiper switching relay 253 is energized through wiper 270 as soon as the wipers 269-272 reach an idle trunk line, whether the trunk line then engaged by wipers 266-268 is idle or not. It will be understood, of course, that if the trunk line engaged by wipers 269-272 is in use, while the` trunk line engaged by wipers 266-268 is idle, relay. 253 is not operated, and relay 252 operates through wiper 267 to seize the trunk line accessible to the upper wiper set. Assuming that the wipers arrive upon the bank contacts terminating ythe trunk lines comprising conductors 281-283 and 284-286 at a time when the trunk line comprising conductors 284-286 is idle, relay 253operates.

Upon operating, relay 253 closes a locking circuit for itself at its lower contacts by'way of off-normal contact 261; opens the rotary-magnet circuit at its middle lower armature; shifts the upper winding of relay 252 from test wiper 267 to test wiper 270'at its inner upper armature; and at its upperv and lower armatures it'shifts the talking conductor from wipers 266 and 268 to wipers 269 and 272.

At the same time, relay 252 operates sufliciently over wiper 267 to close its locking circuit, in case the upper trunk lineis idle; but, if the upper trunk line is busy, relay 252 waits until wiper 270 is connected up. Upon energizing, relay 252 opens an additional point in the circuit of rotary magnet 262 at its lower armature;`

closes a locking circuit for its lower winding at its inner lower armature, at the same time disconnecting the left-hand terminal ofjthe upper winding of relay 253, so as to prevent a subsequent energization of relay 253 in case this relay has not operated to switch wipers when relay 252 operates; shifts the incoming releasetrunk conductor at its inner upper armature from in connection with the junctionV of its `lowerwinding and resistance element 258 into connection with wiper 270 by way of inner upper armature of relay 253; and at its upper and lower armatures disconnects the incoming conductors 218 and 220 from magnet 257 and relay 251, and extends them by way of the upper and` lower armatures of the operated relay 253 to conductors 284 and 286, by way of Wipers 269 and 272.

Responsive to the application of ground potential to conductor 285 by way of wiper 270, current flows over conductor 285 and through the common supervisory relay 313, by way of ofi-normal springs 307 and resistance element 306.r Supervisory relay 316 thereupon operates for the usual purpose.

In the connector C1, release relay 301 is operated over conductor 285. Uponoperating, relay 301 opens a point in the circuit of release mag- -net 312 at its lower armature; applies ground :potential to locking conductor 331v at its inner upper armature; prepares a test circuit for the lower winding of relay 305 and a locking circuit for the upper winding rof busy relay 301 at its upper armature; and at'itsinner lower armature` it closes a circuit by way oi oil-normal spring 303 for the lower winding of relay 304. Relay 304 thereuponoperatesand prepares a Vlocking circuit for itself at its inner lower armature, at

-the same time shifting the upper talking conductor, 284, from rotary magnet 309 to vertical magnet 310.

Setting the connector G1 .When the calling subscriber dials the tens digit in the desired number, the consequent seriesof impulses is delivered over conductor rr284 by way of armature 332 and its resting contact and the inner upper armature of relay 304 to vertical vmagnet 310. The circuit of vertical magnet 310 includes conductors 284 and 286 in series, conductor 236 being connected tothe grounded holding conductor 331 in the connector by way of the low resistance series relay 303 and contacts of relays 302 and 305. By the operation of magnet `310, the Wipers 317-319 are raised step bystep until they come to rest opposite the desired level of bank contacts. When off-normal spring 307 operates, upon the rst Vertical step of the switch, it shifts the circuit of the relay 316 from the incoming conductor 285 to the control of busy relay 302 at its inner upper armature.

`Series relay 303 operates responsive to the first 'Y impulse of current delivered to magnet 310, and

it remains'operated throughout this series of impulses because of the inter-impulse current-now permitted over the lower 4talkingconductor yby virtue of the above-mentioned connections made at the cnice selector OS to the lower talking conductor by way of resistance elements 125 and 126. When it operates, series relay 303 completes a locking circuit for the lower winding of ringcut-oi relay, 304 at its inner lower armature, thereby maintaining relay 304 operated after its initial 'circuit has been opened at off-normal spring 308.

locking circuit of relay 304 at its inner lower armature, whereupon relay 304 falls back and shifts the upper talkingV conductor from vertical magnet 310 to rotary magnet 309.

When the calling subscriber vdials the nal digit, the consequent impulses are deliverednover conductor 284 to rotary magnet 309 by way of contacts of relays 305, 304, and 302. By the operation of the rotary magnet, the wipers 317-319 are rotated step by step over the bank contacts in the selected level until they come to rest upon the bank contacts connected to the called line. The series relay 303 is again operated throughout the series of impulses. At its inner upper armature, relay 303 disconnects test wiper 318 from the lower winding of switching relay 305 and vconnects' it instead to the upper winding of busy relay `302; and at its upper and lower armatures it shunts the resting contactsl of the upper and llower armatures of busy relay 302 so as to maintain-the impulsing circuit intact in case busy relay 302 energizes during rthe rotary movement because of wiper 318 passing over busy test contacts.

The operation taking place at the end of the rotary movement Vdepends upon whether the called line is busy or idle, as will now be pointed out:

Called Zine busy Assuming that the lineof substation A2 is busy when called, test wiper 318 encounters a ground potential on conductor 321 through the associated test Contact, and busy relay 302 vis energized through its upper winding and test wiper 318 when the wipers come to rest upon the desired set of bank contacts. With busy relay 302 energized, the falling back of series relay 303 results in'a locking circuit being closed for the upper winding of busy relay 302 at the normally closed contacts controlled bythe inner upper armature of relay 303. This locking circuit includes the middle upper armaturevof busy relay 302, armature 334, and the upper armature of release relay 301. With busy relay 302 operated, a`

connection exists between the busytone conductor 314 and the lower talking conductor 286 at the lower armature of busy relay 302 and byway of the inner lower armature of switching relay 305. By virtue of this connection, a busy signal is transmitted back to the calling line. Upon hearing thisy busy tone, the callingsubscriber is expected to replace his receiver and bring. about the release of the operated switches in a manner similar to that to be hereinafter described.

It will be noted that magnet 309 and relay 303 are disconnected at the upper and lower armatures of relay 302.

winding of switching relay 305 through test wiper 318, which circuit is as follows: from ground by way of the upper larmature of release relay 301, armature 334, normal, middle upper armature,

normal, of relay 302, lower winding of rela`y`305, inner upper armature of relay 303, test wiper 318, and thence by way of the test contact on which wiper 31S is standing and conductor 321,.to battery through the usual cut-off relay associated with the called line. Responsive to the currentow through its lower winding, relay 305 operates and closes a locking circuit for its upper Winding at its inner upper armature; prepares a locking circuit for the lower winding of ring-cut-oi relay 304 at armature 335; at its inner lower armature it disconnects the lower talking conductor from series relay 303 and extends it to the disconnected lower winding of busy relay 302; disconnects the upper conductor from the rotary magnet at arma* ture 332; connects up the wipers 317 and 319 at its upper and lower armatures; and at armature 334 it opens a point in the regular locking circuit of the upper winding of busy relay 302 and closes a circuit for the upper winding of busy relay 302 which includes the upper armature of relay 301. Busy relay 302 is thereby operated in preparation for the holding of the connector C1 under the control of the called line in case the calling subscriber is the first to replace his receiver.

The busy tone is not sent back to the calling line at this time because the busy-tone circuit includes the resting contact of the inner lower armature of the now-operated relay 305.

Signalling the called subscriber With the wipers connected up at the upper and lower contacts of switching relay 305, ringing current now passes from the common generator lead 315 to the upper conductor 320 of the called line by way of the upper winding of ring-cutoff relay 304 and the upper armatures of relays 304 and 305. A return path to ground is provided for the ringing current by way of the lower talking conductor 322 and the lower armatures of relays 305 and 304.

The called subscriber answers When the called subscriber responds to the ringing of his bell by removing his receiver, the ring-cut-ol relay 304 is operated over its upper winding in the usual manner. Upon operating, relay 304 completes its locking circuit at its inner lower armature to conductor 331 by way of armature 335, and at its upper and lower armatures opens the ringing circuit and connects the wipers 317 and 319 to the incoming talking conductors 284 and 286.

In the oilice selector OS, back bridge relay 113, which is bridged across the wiper side of the talking condenser-s in series with the exchange battery, now operates in Yseries with the telephone instrument at substation A2. Upon'operating, back bridge relay 113 opens the locking circuit of the slow-acting meter-control relay 116 at its lower armature, and at its upperarmature it connects the ungrounded terminal of a source of positive potential by way of lresistance 119 to the incoming releasetrunk conductor 10Q, at the same time disconnecting release-trunk conductor by the momentary application of positive potential to conductor 109, the marginally adjusted meter M operates to register the answered call.

The two subscribers may now converse with each other as desired.

Release of established connection; calling sub scriber replaces receiver first Itwill now be assumed that the called subscriber is the rst to replace his receiver when the conversation is terminated. Under this condition, when line relay 111 of the oilice selector OS falls back responsive to the receiver being replaced, it closes the usual bridge across the wiper side of the talking conductors at its lower contacts. Since back-bridge relay 113 is already in operated condition, the talking current is merely shunted away from the called line by this local bridge, At its inner contacts, line relay 111 places the usual shunt around release relay 114, but series relay 117 does not respond at this time, as it has been disconnected upon the falling back of the meter-control relay 116, above described.

After a slight interval, release relay 114 falls back responsive to the shunt being placed around its winding at the contacts of relay 111. Upon falling back, relay 114 opens its locking circuit at its inner lower armature; opens the local bridge across the talking conductors at its lower armature; removes ground potential from test wiper 130 at its inner upper armature, thereby bringing about the release of the switches of the train in a manner to be explained; removes ground potential from the incoming releasetrunk conductor 109 at its middle upper armature, thereby permitting the line switch LS to release; opens the locking circuit of relay 118 at its middle lower armature; and at its upper armature it closes a circuit for release magnet 120 which includes contacts of relay 112 and off-normal contacts 121. Release magnet 120 operates to restore the oice selector OS to normal position, whereupon the release-magnet circuit is opened at OIT-normal contacts 121.

Switching relay 118 having fallen back responsive to the opening of its locking circuit at the middle lower armature of release relay 114, the oflice selector OS is now in normal position, as back bridge relay 113 is deenergized responsive to the wipers being disconnected at the upper and lower armatures of relay 118.

As a result of the holding potential being removed from the release trunk conductor of theI established connection at the inner upper armature of release relay 114 of the oflice selector OSI the upper windings of relays 201 and 251 are no longer short circuited, whereupon they are energized in series with the lower windings of relays 202 and 252, respectively. At the same time, sufficient current flows over the release trunk conductor of the established connection from ground by way of the windings of relays 201 and 251 to maintain release relay 301 of the connector C1 operated for the time being.

In the thousands selector Th.S1,-the energize.- tion of relay 201 results in the closure of a circuit for release magnet 208 at the lower armature of the relay and through the lower armature of the operated relay 202, While in the hundreds selector HSl the energization of relay 251 results in the closure of a similar circuit for release magnet 260. Release magnets 208 and 260 thereupon both operate, restoring the selectors Th.S1 and HSl to normal position. When the selectors reach normal position, the relaycircuits are opened at offnormal contacts 203 and 254, whereupon relays 201, 202, 251,-nand`252`fall back, opening the circuits o'f release magnets -208 and`260.

In the connector C1, release relay 301 falls back responsive to wiper 270 leaving the contact on which it has been standing. When relay 301 falls back, it closes a point inthe `circuit of release magnet 312 at its lower armature, but release magnet 312 is controlled Valso at the inner lower armature of busy relay 302, which is now operated; and at its upper armature it opens the initial circuit of the upper winding of busy relay 302. Busy relay 302, however, does not fall back at thistime,'but remains operated over the called line (it having been assumed hereinbefore that theV receiver is still off the hook in the called substation), because a holding circuit is closed to the called line for the upper and lower windings of -busy relay 302 in series at the upper contacts of relay 301 and at the contacts controlled by the innerlower armature of the relay. The lower winding of relay 302 is now connected between ground and the lower talking conductor by way of the inner Lipper armature of -relay 302,` armature 335, inner lower armature of ring-cut-oif relay 304, and the contacts controlled by the inner lower armature of relay 301. At the same time, the upper winding of relay 302 is connected between the ungrounded pole of the exchangebattery and the upper talking conductor by way of the operated armature 334 of relay 305 and the contacts controlled by the upper armature of relay 301. As long as busy relay 302 remains operated over the called line, it maintains ground potential on-conductor 331, thereby maintaining relays 304 and 305 operated. By maintaining a guarding ground potential on conductor 331 at armature 333, relay'305 maintains the called line guarded, and it thereby prevents a false operation of the line switch (not shown) individual to the called line. Also, the connector Cl is in a guarded condition, since the battery potential applied to conductor 285 throughrelay 301 is insufficient to mark the incoming trunk line idle, because of the relatively high resistance of the relay winding.

Thecalled, Vsubscriber replaces his receiver Whenthe called subscriber replaces hisreceiver, busy relay 302 "falls back and removes ground po-V tential from conductor 331 at its inner upper armature, permitting relays 304 and 305 to fall back. At its innerllowerarinature, relay 302 closes a lcircuit for release magnet 312, whereupon `release magnet -312 restores the connector C1 to normal position. The circuit of release magnet 312 is thereupon opened Aat orf-normal spring 308. Y The entire 'connection is now released and all the apparatus involved therein is in readiness to be used in setting up subsequent connections.

Release of the established connection when the calledl subscriber hangs up first lease magnet 312, as busy relay 302 is not maintained operated over the called line.

I hter-olce call from the subscriber at substation A1 to the subscriber at substation A3 It Will now be assumed that the subscriber at substation A1, Fig. 1, desires to converse with the subscriber atsubstation A3, whose line terminates in a distant office of the system. Assuming that the line switch LS extends the calling line to the oiiice selector OS when the receiver is removed, the office selector OS is prepared for operation in the hereinbefore-described manner and dial-tone current is transmitted back to the calling substation.

Setting the oce selector OS When the rst digit in the desired number is dialled, the oice selector OS responds underl the Ycontrol of vertical magnet 122.as. hereinbefore described by raising its wipers129-131 opposite the desired level of bankcontacts. At the end of the setting operation, the trunk-hunting operation ensues, during whichfwipers129-13l are driven step by step over the selected level of contacts in search of an inter-office trunk line extending to the desired distant office. Assuming that the trunk line comprising conductors `151-.- 153 is the first one found to be idle, this trunk line is taken for use, as the trunk-hunting operatlon is stopped responsive to the operation of switching relay 118 through wiper 130 -and by way of the resistance element associated with conductor 152. v

k As soon as the inter-@flics trunk line is seized. line relay 402 in the thousands selector Th.S2, Fig. 4, operates over conductor 153 in series with the lower winding of back-bridge relay 113` of the office selector OS, Fig. v1.. Back-bridge relay 113 is not operated at this time owing to thehigh resistance of the upper winding or line relay 402.

The two windings of line relay 402 are connectedV between the ungrounded pole of the exchange battery and vconductor 153 by way of the upper contacts of relay.403 and the lower left-hand repeating-coil winding. Line relay 402 closes a circuit through the oir-normal contacts 407 for release relay 401, whereupon release relay 401 operates and prepares circuits at its middle upper and upper armatures for the windings. of

switching relay 406; closes a lockingrcircuit for itself at its inner upper armature independent of off-normal contacts 407; and at its lower armature cpensra point in the circuit or release magnet 411 and prepares a circuit for rotary magnet Setting the thousands selector Th.S2

When the calling subscriber dials the thousands digit in the desired number, the impulses generated at the lower contacts of line relay 111 of the oiiice selector OS are delivered over the upper talking conductor and by way of the interolce trunk conductor 151 to the impulse relay 405 of the thousands selector Th.S2, through the upperleit-hand repeating-coil winding and the inner armature of back-bridge relay 483. The return path for the beginning of the rst in pulseseries relay 1070i the oce selector OS operates as before explained-is to ground at the office selector OS through resistance element 12S. A series circuit over conductors 151 153 is established, however, for the iinal portion of the viirst impulse and for the remaining impulses of the series, as will be pointed out hereinafter.

y304, and 305, and in the immediate operation of re- In the thousands selector Th.S2, each time impulse relay 405 responds to an impulse, it closes a circuit for vertical magnet 409 at its upper armature, which circuit includes the upper and lower armatures of switching relay 406. By the operation of vertical magnet 409, the wipers 418- 420 are raised step by step until they come to rest opposite the desired level of bank contacts. The slow-acting series relay 404 is operated at the inner lower contacts of relay 405 upon the rst impulse, and it remains operated throughout the series. At its inner lower armature, relay 404 places ground potential on the upper ter1ninal of the lower left-hand repeating-coil windn ing, by way of the lower armature Vor release relay 401, thereby extending a ground potential back over conductor 153 to the originating exchange so as to form a loop circuit over conductors 151 and 153 for the delivery of the remaining impulses. This new ground connection is in shunt of the ground connection to the lower talking conductor at the office selector OS by way of resistance element 126.

At the end of the series of impulses, series relays 117 and 404 of the switches OS and Th.S2, respectively, fall back. When relay 404 falls back, it completes a circuit for rotary magnet 416 at its inner lower armature through the inner lower armature of relay 406 and the oinormal spring 415. Rotary magnet 415 thereupon operates in a buzzer-like manner to advance the wipers 418-420 over the bank contacts in the selected level in search of an idle trunk line.

When an idle trunk line is reached, which trunk line it may be assumed is the one extending to the hundreds selector HS2, the upper wind ing of switching relay 406 becomes energize'i through wiper 419,`operating the relay to open circuit of rotary magnet 416 and close a locking circuit for the lower winding through the rotary magnet. At its inner upper armature, relay 406 supplies ground potential directly to wiper 419, and at its upper and lower armatures it disconnects the talking conductors from magnet 409 and from ground and extends them by way of wipers 418 and 420 to the hundreds selector H52.

Setting the hundreds selector HSZ When the hundreds digit is dialled, the consequent impulses are repeated by the oflice selector OS to the impulse relay 405 of the thousands selector Th.S2, whereat the impulses are repeated at the upper contacts of relay 405 to the hundreds selector HS2.

The hundreds selector HSZ, which may be the same as the selector Th.S1, Fig. 2, responds to the received impulses by raising its wipers opposite the desired level of bank contacts and in rotating them over the selected level of bank contacts in search of an idle trunk line. It will be assumed that the trunk line extending to the connector C2 is `the iirst one found to be idle, in which case this trunk line is seized and the r connector C2 is prepared for operation as explained in connection with the connector C1, Fig. 3.

Setting the connector C2 contact connected with the line of substation A3. If the line is busy, a busy-tone current is transmitted back tothe calling lineas explained in connection with the connector C1, but if the called line is idle, the connection is madeY and ringing current is applied to signal the called subscriber.

The called subscriber responds When the called subscriber responds to the ringing of his bell by removing his receiver, the ring-cut-of relay (not shown) in the connector C2 operates in the usual manner to complete .the talking connection, whereupon back bridge relay 403 is operated over the called line. Upon operating, back bridge relay 403 disconnects the battery potential from the upper terminal of the upper winding of line relay 402 and it places the low-resistance lower winding of line relay 402 in shunt of the talking condenser associated with the leftehand repeating-coil windings, at the same time disconnecting impulse relay 405. When this occurs, line relay 402 remains energized over conductors 151 and 153 in series, and back-bridge relay 113 in the oflice selector OS energizes in series with the lower winding of line relay 402 in the distant oflice, with results described hereinbefore.

Releasing the established connection It will be assumed that the subscriber at substation A3 is the first to replace his receiver after the conversation is terminated. When this is done, back-bridge relay 403 of the thousands selector Th.S2 falls back, disconnecting the lower winding of relay 402 from in bridge of conductors 151 and 153 and again connecting the upper terminal of the upper winding of line relay 402 to battery to re-establish the initial holding circuit of the line relay. When this occurs, backbridge relay 113 of the office selector OS falls back because of the high resistance of the upper winding of line relay 402.

When the subscriber at substation A1 replaces his receiver, line relay 112 falls back and places a bridge across the wiper side of the talking conductors, re-operatng back-bridge relay 113. At the same time, release relay 114 is shunted at the inner contacts of relay 111, causing release relay 114 to fall back and bring about the release of the oiiice selector OS as hereinbefore described.

In the thousands selector Th.,S2, line relay 402 falls back and opens the circuit of release relay 401. After a slight interval, release relay 401 of the thousands selector Th.SV2 falls back and removes ground potential from wiper 419 at itsv upper armature; opens the locking circuit of switching relay 406 at its middle upper armature; opens a further point in its own circuit at its inner upper armature; and at its lower armature it closes a circuit for release magnet 411 through oil-normal springs 410. 'By the operation of release magnet 411, the thousands selector Th.S2 is restored to its normal position in the usual manner, whereupon the release magnet circuit is opened at off-normal springs 410. It is to be noted that'relay 401 cannot become re-operated, even though the trunk line is again seized in the other oiiice immediately, until the switch is restored to its normal position and a circuit is prepared for relay 401 at off-normal contacts 407.

The selector HS2 andthe connector C2 are released in the manner explained in connection with the switches of Figs. 2 and 3.

Supervising the olice selector OS erates, relay 116 closesl a circuit at its lower ar- Y `mature by way of ofi-normal contacts 123 and over the common conductor 133 for the' first siipervisory signal. This circuit opened as" on as the oiiiceA selector OS is moved from its no Ll position. By observing this signal, an attendant can determine whether or not there is an of? selector in a seized and unoperated condition.

It will'be recalled also that the lmeter-control relay 116 is deenergized following the operation of back-bridge relay 113 whenl the call is answered. With relay 116 in normalposition, the falling back of back-bridge relay 113 responsive to the called subscriber replacing his receiver before the calling subscribery does so resultslinthe closing of a circuitover the second supervisory conductor 134 .at the lower` contacts( of backbridge relay 113. This kcircuit includes off-normal spring123 and its upper Contact, andthe inner lower armature of relay 116. This circuit is opened as soon as the calling subscriber replaces his receiver and brings about the restoration of the office selector OS to normal.

Supervising the intermediate selectors It is to be noted that a supervisory relay 215 is provided common to a plurality of the thousands selectors such as the thousands selector Th.S1. This supervisory relay is operated in series with any resistance element such as resistance elementV 217 when one of the associated thousands selec'- tors is taken f or use. The circuit of relay 213 is opened at oli-normal spring 204 when the thousands selector Th.S1 is operated. In, a similar way, supervisory relay 264 controls the `signal common to the hundreds selectors such as the hundreds selector HSI, being controlled over, thecommon conductor 263 through resistance elements such as the resistance element 259 of the hundreds selector HSL Supervising the connector C1 The connector C1 is supervised in a manner similar to the intermediate selectors of Fig. 2, there being a common supervisory relay 316 controlled over the common supervisory. conductor 313 through resistance elements suchas the resistance element 306 individual to thek connector C1. The supervisory circuit is opened, it will be noted, by busy relay 302 when this relay operates responsive to a busy condition orresponsive to the closing of a local circuit for rit when switching relay 305 operatesresponsive to an idle condition of the called line. By this arrangement, the supervisory circuit is closed rst over the incoming conductor 285 when the sw'itrch'is taken for use, and isY then placed under the control of busy relay 302 as soon as ofi-normal springs 307 operate, and` it remains closed until connection is completed to an idle line or until the called line is found to be busy. In this way, the supervisory signal controlled by relay 316 indicates whether or not there are any connectors in a seized position which'h'ave not been completelyoperated.

Supervising the incoming thousands selector Th.S2

When the release relay 4401 of the thousands selector Th.S2, Fig. v4, operates responsive to the associated trunk line being taken for use, it closes a circuit at'its lower armature by way of the lower armatures of relays 404 and 406 and through off-normal spring 415 and resistance element 417 over the associated supervisory lead to bring about an operation of the connected supervisory signal. This circuit is opened at offnorinal spring 415 as soon as the switch moves from its normal position.

Overfiow at the olice selector' OS In case the cnice selector OS is unable to find an idle trunk line in a selected level, the rotary movementv continues until the wipers 129-131 have been driven beyond the last set of bank contacts, whereupon the overiiow contacts 124 and 128 are closed by the usual cani arrangement carried bythe shaft of the switch. When cam springs 128 close, the lower winding of relay 118 is operated in series with vertical magnet 122, thereby operating relay 118 to disconnect the vertical Vmagnet circuit from the talking conductor and to open the dial-tone circuit. Overflow springs 124 close a circuit path for transmitting busy-tone current by way of conductor 132 to the upper conductor of the called line. Upon hearing the busy tonc,`the calling subscriber is expected to replace his receiver and bring about the release of the oce selector OS in the usual manner.

Overfiow at the intermediate selectors When the thousands selector Th.S1 is unable to find an idle trunk in the selected level, and the overflow springs 209 and 205 are operated, overflow spring 209 removes the shunt from around the lower winding of relay 202 and connects the incoming release trunk rconductor 155 to the junction of thewindings ofrrelays 201 and 202 so as to maintain the upper winding of relay 201 shunted. When this operation occurs, relay 202 operates to open the rotary magnet circuit and thereby stop the rotary movement With overflow contacts 205 closed,v a busy-tone circuit is completed tothe upper talking conductor 154 as soon as relay 202 operates, thereby transmitting a busy tone back tothe calling line to prompt the y calling subscriber to replace his receiver and bring about the release ofthe connection.

An overflow condition at the hundreds selector VI-ISl results in an operation of relay 252 under the control of overow spring 221, which places a new shunt around the upper winding oi relay 251 and removes the shunt from around the lower winding of relay 252. When relay 252 operates to terminate the rotary movement, it completes the busy-tone connection to conductor 218 at its upper armature by way of overow springs 256.

Overflow ai the incoming selector repeater Th.S2

Tandem connections It is to be noted that the incoming thousands selector '13h52, by being equipped with resistance .elements 408 and 412, is arranged in a manner similar to the office selector OS, as regards the repeating of impulses. By this arrangement, a call may be extended from the first oice to the incoming thousands selector Th.S2 inthe distant cnice and thence by way of the incoming thousands selector to a third oii'ice, if the trunking system is so arranged. The third cnice, of course, may be a sub-oflice of the second office. 1n any case, impulses are repeated from the second olice to the third cnice in substantially the same m ner that tiey are repeated from the rst office to `the second oiiice. lt is to be noted. however. that the iirst impulse or" a series repeated by the thousands selector Th.S2, either to an intermediate selector in the same oice or to an incoming selector in a third office, is the same as any subsequent impulse in the series, as the impulse relay 405 is so connected in the impulsing circuit that the first impulse does not await the operation oi' the series relay 494, as in the case ci the selector OS, Fig. 1, wherein the number contacts controlled byline relay 111 must be kept a minimum, and the first impulse awaits the operation of series relay 117.

Switching through at the omcc' selector OS It is customary in telephone syste of the character disclosed herein to arrange the ofiice selector, or iirst selector repeater, so 'that talking conductors may be extended metallicly therethrough and independent of bridges, when the destination or" the call makes this desira'=le, such as, for example, when extendingT a connection to a so-called ring-back switch in a partyline call, and the like.

Trunk circuits which require that the cnice selector be switched through are especially arranged so that a connection is momentarily made therein to the un-grounded pole of the exchange battery by way of a relatively low resistance, thereby bringing about a greatly increased flow of current over the release trunk conductor of the established connection and through test wiper 130 of the office selector OS. This current flow passes through the low-resistance lower winding of the marginally adjusted switch-through Yrelay 112, causing relay 112 to operate. Upon operating, relay 112 locks itself to the grounded conductor 109 at its inner upper armature; extends the grounded conductor 109 through to the test u at armature 161; opens an additional point in the circuit of the release magnet at armature 165i; closes a new holding circuit for the lower winding of switching relay 11S at its inner lower armature; and at its upper and lower armatures it extends the incoming conductors 108 and 110 tothe wipers 129 independent of the talking condensers and cuts oi the front and back bridges, thereby giving an unbridged metallic connection through the selector.

As a result or the frontubridge line relay lll being disconnected, this relay falls back and shunts release relay 114, causing relay llfl to fall back also. No harm results from the deenergization of Vrelay 114 at this time, as the essential work of this relay in maintaining the connection has been taken over by relay 112 as above pointed out. The trunk circuit to which the connection is now extended must be arranged, however, to apply ground potential to the release-trunk conductor immediately after the above-mentioned heavy application of battery potential, thereby maintaining the release-trunk conductor grounded' to maintain the connection intact until the receiver is replaced.

What is claimed is:

1. In an automatic telephone system, an automatic switch having a pair of talking conductors incoming thereto, a separate return conductor, an operating magnet for said switch connected between one talking conductor and said return conductor, a control relay for said automatic switch connected between the other incoming talking conductor and said return conductor, means for transmitting current impulses over the said two incoming talking conductors in series to operate said magnet to position the switch and to operate the controlling relay to control the positioning operation.

2. In an automatic telephone system, an automatic switch having a pair of talking conductors incoming thereto, a separate return conductor, an operating magnet for said switch connected between one ytalking conductor and said return conductor, a control Vrelay for said automatic switch connected between the other incoming talking conductor and said return conductor, means for transmitting current impulses over the said two incoming talking conductors in series to operate said magnet to position the switch and to operate the controlling relay to control the positioning operation, and means effective while a series of impulses is being transmitted for maintaining a reduced current fiow through said control relay and over the associated talking conn ductor during the inter-impulse intervals, Whereby said control relay is maintained operated continuously throughout a series of impulses.

3. in a telephone system, an impulse repeater 'and an automatic switch inter-connected by a vductors to said automatic switch to actuate said operating magnet and for maintaining said battery-feed relay disconnected from in bridge of said talking conductors during the transmission of impulses.

4. In combination, an impulse repeater and an automatic switch inter-connected by a trunk line including a pair of talking conductors, a bridge across said conductors at the repeater for eupplyng transmitter-energizing current, a bridge across the talking conductors at said automatic switch including an operating magnet, means at the impulse repeater for transmitting a series of impulses over said talking conductors to actuate said operating magnet, and means at the impulse repeater actuated throughout the transmission of impulses for disconnecting said current-supply bridge.

5. In a telephone system, an automatic switch having an operating magnet, a talking conductor extending to said operating magnet, a batteryfeed relay having a winding connected between the exchange battery and said talking conductor, means for transmitting a series of impulses over said talking conductor to actuate said operating magnet, and means for opening the connection through said relay winding for the dura/tion of the transmission of impulses to prevent a premature actuation of said relay.

Cil

matic switches to set up the connection7 andl `means in said repeater actuated for the duration of each series of. impulses to `disconnect said battery-feed relay from the talking conductor over which the impulses' are transmitted.

7. In a telephone system, a connector switch having access to subscribers lines, means for operating said switch into association with any line and for completing connection thereto in case the line isidle, a busy relay in said connector actuated responsive to the line being in a busy condition to prevent connection being made therewith and to send back a busy signal to the calling line, means for operating said busy relay Yas a holding relay when connection is completed to a called'line, and meansfor maintaining said busy relay operated over the called line to maintain said connector switch operated after the calling subscriber replaces his receiver in case the called subscriber is the last to replace his receiver.

8. In a telephone system, an intermediate selector having a series relay and a switching relay, means for operating said selector to bring it into association with a desired group or trunk lines and for operating said series relay and for maintaining it operated until the desired group of i trunk lines has been reached, means controlled by said series relay and effective when it restores for causing said selector to search for an idle trunk line in the selected group, a switching relay and means for operating it to seize an idle trunk when one is found, a release magnet for restoring said selector to its normal position, means for operating both of said relays to restore the selector, and an operating circuit for said release magnet including contacts of both relays in series and closed only when both relays are actuated.

9. In an yautomatic switch, a rst relay and means for operating it momentarily while the switch is being positioned, a second relay and means for operating it after the -switch has been positioned, means eiective when the switch is to be restored to normal position for maintaining the second relay operated and `for re-operating the first relay, and means responsive to both relays being operated at the same time for restoring said switch to its normal position.

10. In a telephone system, an automatic switch having two sets of wipers, two groups of trunk lines accessible to said wiper sets respectively, one set of said wipers being normally connected up to the switch for use, while the other set of wipers is normally disconnected, and means effective whenever the trunk line engaged by the normally disconnected set is idle for substituting the normally disconnected set of wipers for the normally connected set.

l1. In an automatic telephone` system, an automatic switch having two sets of wipers, trunk lines arranged to be tested over by said wiper sets, two test relays associated with said wiper sets respectively, means for advancing said wipers until an idle trunk line is found by either or both sets, means for operating the rst test relay through a wiper in therst set in case the trunk ine encountered thereby is idle, whereby aV connection `is made to the trunk line engaged by the iirst set of wipers by way of normally open con- .tactsof the' iirst test relay and normally closed contacts of the second test relay, and means for operating thesecond test relay over a wiper in the second set in case the trunk line encountered thereby isA idle and whether the trunk line encountered by the first set is busy or idle to seize the trunk line encountered by the second wiper set through normally open contacts ci both test relays, and means responsive to the operation of either. test relay for stopping the advance of the wipers.

l2. In a telephone system, a trunk line comprising a .pair of talking conductors andextending to an automatic switch, an impulse relay in said automatic switch controlled over the rst of said talkingconductors, a holding relay in said automatic switch controlled over the second talking conductor, means for taking said trunk line for use and for sett'ng up a current flow over the second talking conductor to operate said holding reu lay and to maintain it operated for thepurpose oi holding said automatic switch after it has been operated, means for transmitting a series of impulses cver the rst talking conductor to operate said impulse relay to bring about the setting of said automatic switch, a resistance element, circuit arrangements for transmitting the first impulse of current over said rst talking conductor and through said resistance element in a circuit path independent of the second talking conductor, and means in said automatic switch responsive to said first impulse of current for placing the second talking conductor in shunt of said resistance element, whereby the remaining impulses are transmitted over the two talking conductors in series to said impulse relay.

13. In a telephone system, a two-conductor trunk line extending to an automatic switch, an impulse relay in said automatic switch connected to the rst of said conductors and arranged to repeat impulses -from the conductors to the automatic switch, means Afor transmitting a series of impulses over said conductors to said impulse relay to bring about an operation of said switch, a resistance element, circuit connections for transmitting the rst impulse over the irst conductor through said resistance element an`d independent of the second conductor, and means responsive to the transmission of the first impulse for placing the second conductor in shunt of said resistance element to enable the subsequent impulses to be transmitted over the two conductors in series.

14. In a telephone system, a two-conductor trunk line extending to an automatic switch, a holding relay in said automatic switch connected to the second of the trunk-lineconductors, means for delivering operating impulses to said automatic switch over the rst of said trunk-line conductors,l means for maintaining the holding relay operated over the other of said conductors to` maintain the switch in its operated position, and means effective ,in .said automatic switch while the setting impulses are being received for closing a localV holding circuit for said holding relay independent of the second conductor.

15. In an automatic multi-exchange telephone system, a.trunk line extending from Aa first olce to a second cnice, means for transmitting a series of setting impulses from the first olce to the second oice over one conductor of said trunk line,

means in the rst oiice for making an application o ground potential to the second talking conductor to enable the iirs't impulse of a series to be delivered to the second oiiice over the irst talking conductor and through a bridge across the .talking conductors and said ground connection,

and means in the second oihce responsive to the rst impulse for making a ground connection to the second talking conductor in the second office in shunt of the irst-named ground connection in order to enable the subsequent impulses to be delivered to the second omce over the two conductors in series.

16. In an automatic telephone system, a selector switch, a trunk line incoming thereto including a pair of talking conductors, an operating magnet for said switch, a control relay for said switch, a circuit for said magnet andrelay including the two talking conductors in series, and an auxiliary holding circuit for said control relay including only one oi said talking conductors and ground.

17. In an automatic telephone system, an impulse repeater and an automatic switch interconnected by a pair of talking conductors, an operating magnet and a change-over control relay bridged across the talking conductors at said switch in series with the battery, a line relay at the repeater, a bridge closed across the talking conductors by said line relay each time it deenergizes in repeating a series of impulses, said bridge completing a circuit for operating said magnet and changeover relay in series, and means controlled by the line relay each time it energizes in repeating a series of impulses for closing an auxiliary circuit over only one talking conductor to maintain said changeover relay energized.

18. A selector switch having a directive primary movement and an automatic secondary movement, said selector having only two relays, means for energizing the first relay during the primary movement and for deenergizing it at the end thereof to start the secondary movement, means for energizing the second relay to stop the secondary movement, and means for energizing both relays to release the switch.

19. A two motion selector switch having a combined changeover and release relay, means for energizing said relay during the primary movement and for deenergizing it at the end thereof to start the secondary movement, a circuit closed on completion of the secondary movement for again energizing said relay to release the switch, a release conductor, and connection from said conductor to said relay circuit whereby a holding potential on said conductor prevents said relay from energizing.

2i). In a selector switch, a wiper connecting relay, a test conductor on which a potential is maintained to hold said relay energized, a release circuit prepared by said relay, and a second relay which is shunted by said potential and which energizes in series with saidrst relay when the potential is removed to complete said release circuit.

21. In a selector switch, a test conductor on which a potential may be maintained to control the release of the switch, a relay, means for closing a circuit for said relay when the switch is operated, a connection to said circuit from said conductor whereby the potential thereon prevents the relay from energizing, and a release circuit controlled by said relay when it energizes responsive to the removal of said potential.

JOHN WICKS. 

